Tanning-liquor



UNITED STATES PATENT OFFICE.

MARTIN DENNIS, OF NEWARK, NEW JERSEY.

TANNING-LIQUOR.

SPECIFICATION To all whom it may concern.-

Be it known that I, MARTIN DENNIS, a citizen of the United States, residing at Newark, 1n the county of Essex and State of New J orsoy, have invented certain new and useful Improvements in Tanning-Liquors, of which the following specification is a full, clear, and exact description.

My invention relates to a liquor to be used in the tanning of leather.

It consists of a novel composition of matter in a liquor for tanning hides or skins in the method known as chrome tanning, and the method of making the same.

In an application filed by me on the 3d day of October, 1892, Serial No. 447,695, I have described and claimed the use of this liquor which is the subject matter of this application, in tanning hides, and this application has therefore no reference to the methods of using this liquor, but relates solely to the composition of the liquoritself and the method of making it.

It has long been known that chrome oxide has the property of combining with the hide gelatine to form an insoluble and non-putrescent body, and is therefore capable of converting hides into leather. It has only been during the last few years, however, that commercial leather has been made by the socalled chromio tannage and there is still much room for improvement. I

The difficulty standing in the way of the use of chromic oxide as a tanning agent, has been its insolubility in water, and the consequent difiiculty in getting the chromic oxide into intimate contact with the hide or skin to be tanned. Attempts have been made to overcome this difficulty by the use of chromic alum as a tanning agent, but without practical success. When chromic alum is used deoxidation or reduction is unnecessary since the chromium exists in the alum in the form of an oxide, but as chromic alum is a very stable body and gives up its chromic oxide with great difficulty, the process of fixing the hide gelatine by its use is exceedingly slow, unsatisfactory and expensive. This difficulty has been in a measure overcome in some processes, by. impregnating the hide or skin with chromic acid, and then reducing forming part of Letters Patent No. 511,411, dated December 26, 1893.

Application filed April 10, 1893 Serial No. 69,793- (N0 specimens.)

this chromic acid to ch'romic oxide in the substance of the hide by the use of some reducing agent, as for example, sulphurous or ing and corrosive agent and invariably does more or less injury to the hideor skin, and unless it is handled with very great skill and caution, will produce leather which will become hard and crack and exhibit other defects. In fact the utmost care and experience often fail to prevent the finished leather from showing the destructive effect of this powerful corrosive agent. One of the probable causes of the deterioration of leather made by the use of chromic acid is that chromic acid itself appears to enter to a greater or less extent into some sort of combination with the hide gelatine, in which combination it is not wholly reduced to chromic oxide by the sulphurous acid or other reducing agent' its losing its strength and suppleness and becoming hard and brittle and papery to the touch. The unsatisfactory action of chromic alum in tanning and the destructive efiect of the chromic acid upon the fiber of the hide or skin therefore renders it highly desirable to employ some method of chrome tanning which will be quicker and cheaper and more satisfactory than the use of chromic alum and which will not necessitate the bringing of the hide or skin into contact with these strong and corrosive acids. The object of my experiments was therefore, to, discover some method of introducing chromic oxide to the hide or skin to be tanned in a water soluble, neutral and unstable combination, that is, to discover some chromic oxide compound soluble in water, in which the chromic oxide would be held loosely, that is, in an unstable combination, and which compound when dissolved would be practically neutral, and I tirely basic.

have succeeded in doing this by my invention, which I will now describe.

It is well known that when to solutions of a number of the normal salts of chromium is added a quantity of a more powerful base, a part of the acid which was combined with the chromium base is taken away and the chromium base is leftin a combination which may be regarded as basic, that is, containing two or more equivalents of the metallic base or oxide to one of the acid, and when in this condition the excess of the metallic base or oxide over what the acid would hold in the normal salt is readily yielded to any body having an affinity for it, that is, the excess of the metallic base or oxide over what would be present in the normal salt is held in an unstable combination with the normal salt. WVhile this is a well known chemical fact, it was not known prior to my discovery or invention that any commercial use could be made of this chemical property of the salts of chromium in chrome tanning.

In preparing my tanning liquor according to this invention, I utilize this property of chromium salts. I have found chloride of chromium best adapted for my purposes, although other inorganic salts of chromium may be used with more or less success, and I prefer to use chloride of chromium in practicing my invention and shall use it hereinafter in illustrating the same.

In practicing my invention, I first prepare a solution of common chloride of chromium. This may be done by dissolving the commercial oxide of chromium in commercial hydrochloric acid, which has been diluted with an equal bulk of water, care being taken to use more chromic oxid'e than the acid will take up, in order that the resulting solution may be as nearly neutral as possible. About eight ounces of the commercial acid is sufficient to dissolve a pound of commercial oxide of chro' mium. When this reaction is complete I have the normal salt of chromium known as chloride of chromium, in solution. In order to render this normal salt of chromium a basic salt I add slowly and carefully to this solution a solution of a more powerful base, continuing the addition to a point where the normal salt has been practically rendered en- This point will diii'er in different cases depending in a measure on the strength of the solutions, but the addition shouldnot be carried beyond the point at which the oxide of chromium begins to precipitate, and the amount of base to be added can be readily ascertained in each case by making a small experimental mixture. I may use for this more powerful base any of the caustic alkalies or the carbonates of these alkalies,

it may be added until rapid efiervesence ceases. It usually takes about a half a pound of sal soda crystals to each pound of chromic oxide dissolved as above. When this reaction is complete it will be found that the carbonate of sodium has changed the normal chloride of chromium into an oxy or basic chloride of chromium. This may be considered as consisting of the normal chloride of chromium and chromic oxide in a water soluble combination, (free chromic oxide, hydrated orotherwise being insoluble in water.) This oxy or basic chloride of chromium 1s avery unstable body, giving up its excess of chromium oxide whenever there is presented to it a body or substance for which chromic oxide has an affinity (as for instance hlde gelatine). There exists also in this solution when i the last reaction is completed a quantity of chloride of sodium formed by the union of a part of the acid which was in combination with the chromium in the normal salt of chromium with the sodium base of the carbonate of sodium. This chloride of sodium serves the useful purpose of preventing the gralnof the leather from drawing under the astringent effect of the chromium salt and facilitates the tanning action, and to further effect these purposes I also add to this solution a few pounds more of chloride of sodium (common salt). When I use any of the alkal es or alkaline carbonates that do not contain soda, I prefer to add to the solution common salt. When this has been done my tanning liquor is complete and ready for use in the manner indicated in my aforesaid application.

I am aware that others have added carbonate of sodium to the solution of a chromium salt, but in all cases where this has been done only so much carbonate of sodium has been added as would serve to take up the free acid in the solution of the chromium salt and thereby neutralize the solution, and in no case has carbonate of sodium been added to the solution of the chromium salt in an amount sufficient to affect or change the chromium salt in any particular, or for that purpose, while in my invention that is one of the principal objects of adding the carbonate of sodium, as my solution is practically neutral, before its addition.

The tanning liquor produced by this invention, is cheaper and more quickly and easily used than a liquor made from chromic alum; is practically neutral, has no corrosive action on the hides, and is free from all oiIensive odors, in these particulars as well as others being a marked improvement on all known tanning liquors.

In the foregoing specification and in the claims to follow, the term basic is meant to include metallic salts, which contain more than one equivalent of the metallic base to one equivalent of the acid, as above described, and in the claims, the term carbonate of sodium is meant to include its chemical equivalents for the purpose specified.

The word tanning is meant to include all methods of fixing or rendering insoluble the so-called gelatine of the hides or skins for the purpose of converting them into leather.

My invention consists broadly in a method or process of making a tanning liquor, containing a basic or oxy-inorganic salt of chro-' mium and the product of that process.

Specifically it includes a method or process of making a tanning liquor containing a basic or oxy-chloride of chromium and chloride of sodium, and the product of that process.

I therefore claim 1. The process of making a tanning liquor which consists in taking a solution of a normal inorganic salt of chromium and rendering the normal inorganic salt basic by the addition to the solution of a solution of the alkalies or the alkaline carbonates, substantially as described.

2. The process of making a tanning liquor which consists in taking a solution of normal chloride of chromium and rendering the normal chloride of chromium basic by the addition to the solution, of a solution of one of the alkalies or alkaline carbonates, substantially as described.

3. The process of making a tanning liquor which consists in taking a solution of normal chloride'of chromium and rendering the normal chloride of chromium basic by the addition to the solution of soda or carbonate of soda, substantially as described.

4. The process of making a tanning liquor which consists in dissolving chromic oxide in hydro-chloric acid and then rendering the resulting chloride of chromium basic by the addition of soda or carbonate of soda and then adding chloride of sodium, substantially as described.-

In testimony whereof I have signed this specification in the presence of two witnesses.

MARTIN DENNIS.

Attest:

J. D. GALLAGHER, H. E. RICHARDS. 

